I know you know a lot about the language already which I don't, but thought I'd post this here, which turned up on a search on the phrase, similar spelling to the one used by Sean OL in his search of twexus.
From Steve Quayle's site
"Alhaam hu Akhbar" is a "decree or order of Allah" to overthrow the infidels through murder, suicide, and any method possible. It is a similar pronouncement given in 'Allah' hu akhbar," (Allah, or God, is great).